It’s an amazing journey for most tropical fish starting out life as larvae floating in the open ocean to making it back to the coast to settle down and live out the rest of their days.

During this process many species undergo rapid and often radical changes in their appearance changing from transparent larvae to the beautiful diversity of shapes and colours we are most familiar with.

Understanding when, where and how many tropical fish settle into different Kimberley habitats will provide an important management tool to help protect essential nursery areas and ensure there are plenty of reproductive adults to resupply following generations.

Alongside the Bardi-Jawi Marine Rangers and Traditional Owners, a WAMSI team from the Australian Institute of Marine Science (AIMS), CSIRO, Western Australian Museum and Departments of Fisheries and Parks and Wildlife, began surveys of fish recruitment in April.

Diversity of larval fish (and other) forms captured from the open ocean. Image from Robert Cowen Laboratory, University of Miami, USA.

“The first stage was to develop the right technique to do this accurately in the challenging Kimberley environment,” AIMS researcher Martial Depczynski explained.

“We assessed nine different methods among seagrass, coral reef, inter-tidal and mangrove habitats typical of the Kimberley region.

“We found in most cases that different nursery habitats were best quantified using different methods but that one single method was sufficiently efficient, easy, cost-effective and safe to use in all four habitats,” Dr Depczynski said.

Lifecycle of a juvenile reef fish. Fish begin their lives in the open ocean as semi-transparent larvae before recruiting and settling into their juvenile and adult coastal habitat often for the rest of their lives. During recruitment, they undergo metamorphosis losing their larval features to take on their characteristic shape and colouration. Image from Reefkeeping South Africa.

The investigators found that remote underwater video, although new to the task of recording small juvenile fishes, was able to provide robust relative estimates of abundance and diversity in fish nursery habitats and was the best option among the nine methods.

“Now that the correct methodology has been developed, our next trip in October, which will run in conjunction with a team investigating the same recruitment process in corals, will concentrate on getting a solid data set together to answer questions such as; what nursery habitats are important to what fish species, are there hotspots of fish recruitment activity and what is the strength of fish recruitment in dry versus wet seasons,” Dr Depczynski said.

“We will continue to work in with the Bardi-Jawi Marine Rangers and the Traditional Owners on the Cape Leveque – Sunday Island – Cygnet Bay area to better understand the processes that govern fish recruitment processes in this area.

“The main aim and best possible outcome from this WAMSI project is to have definitive quantitative data on fish and coral nursery areas which identify nursery hotspots and can feed into both State and Indigenous management plans such as the next Bardi-Jawi Indigenous Area Management Plan.

Remote underwater video unit deployed to record newly recruited fishes in an intertidal rock pool during low spring tides on Sunday Island.

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley. 

 

Kimberley Marine Research Program